NASA Instruments Will Listen for Supersonic X-59’s Quiet ‘Thump’

from NASA X-59 The experimental plane is unique: it is designed to fly faster than the speed of sound, but without causing a loud sonic boom. To confirm the X-59’s ability to fly supersonically while only producing quiet sonic “thumps,” NASA needs to be able to record these sounds from the ground. The agency recently completed testing aimed at understanding the equipment and procedures needed to make those recordings.

NASA’s Carpet Determination in Complete Measurements (CarpetDIEM) flights examined the quality and robustness of a new generation of ground recording systems, focusing on how to deploy the systems for X-59 testing and recover the data they collect . In total, researchers set up 10 microphone stations across a 30-mile stretch of desert near NASA’s Armstrong Flight Research Center in Edwards, California.

“We’re trying to answer questions like how many people are needed to go out and service these instruments on a daily basis, how to retrieve the data, how many vehicles are needed, all those kinds of things about how we operate,” said Forrest Carpenter, principal investigator for the third series of flights, known as CarpetDIEM III. “Now we’re learning to dance so that when we get to the big dance, we’ll be ready to go.”

The 4, at altitudes ranging from 40,000 to 53,000. feet. Three of the passes involved an F-18 performing a special inverted dive maneuver to simulate a silent sonic boom, and one of them reached a perceived noise level of 67 decibels, a measure of the plane’s perceived noise by an observer in land.

“We expect the sonic punch from the X-59 to be as low as about 75 decibels of perceived loudness,” said Larry Cliatt, subproject manager for Questt’s acoustic validation phase. “That’s much quieter than the Concord, which had a perceived loudness of over 100 decibels.”

To measure these very quiet sonic booms, the ground recording systems used on CarpetDIEM flights were calibrated to measure just about 50 decibels of perceived loudness, the equivalent of being in a room with the refrigerator on.

CarpetDIEM III also validated the use of automatic transmission-dependent surveillance, an existing technology used on all commercial aircraft and most private aircraft to report speed and position. This system activates the ground recording systems to begin recording.

“We can’t have 70 different people in each instrumentation box,” Cliatt said. “We had to find a way to automate that process.”

The recording systems are designed to withstand the desert elements, extreme summer heat and winter cold, and to be resistant to wildlife damage such as chewing by rodents, coyotes and foxes.

“When we get to Phase 2 of the Questst mission, we expect to make these sonic knock recordings for up to nine months,” Cliatt said. “We need to be able to have instrumentation and operations that can facilitate such a long deployment.”

Another lesson learned: Setup time for the recording stations was just under an hour, compared to the planned two and a half hours. Given the performance of the systems, the team will evaluate whether it is necessary to visit all sites every day of the Phase 2 test.

The team also learned about the coordination and documentation processes necessary for such research, both with internal organizations, such as NASA’s Armstrong Environment and Safety offices, and with external parties, including:

• The U.S. Bureau of Land Management, which approved the use of public lands for testing.
• Law enforcement, who helped secure the test site.
• The Federal Aviation Administration, which approved NASA aircraft to fly outside the restricted airspace of Edwards Air Force Base to conduct a portion of the CarpetDIEM testing.

To prepare for Phase 2 of Questst, researchers hope to conduct practice sessions in 2024, incorporating all the lessons learned and best practices from all three phases of CarpetDIEM.